Calix[4]arene-based Supramolecular Gels for Mercury Ion Removal in Water.

A calix[4]arene-based gelator 1, with lower-rim mono triazolylpyridine group, capable of spontaneous self-assembly into microspheres in different ethanol/H2 O mixtures, is synthesized. The concentration-dependent 1 H NMR spectra and X-ray single-crystal structure of 1 provided evidence for self-assembly of gelator 1 via cooperative interactions of intermolecular noncovalent forces. Furthermore, metallogels by self-assembly of 1 was found to exhibit remarkable selectivity toward Hg2+ ions. 1 H NMR spectra support that Hg2+ ion was bound to the nitrogen atoms of two coordination sites of 1, which composed of triazole and pyridine. Moreover, the results of field emission scanning electron microscopy and rheology experiments indicated that Hg2+ ions not only enhanced the gelling ability of gelator 1 in ethanol but also led to morphological change of its self-assembly through metal-ligand interactions. Finally, the in situ gelation, triggered by mixing a gelator solution of 1 in ethanol with water samples such as deionized (DI), tap, and lake water, leads to the effective removal of Hg(II) from a water sample which reduced from 400 to 1.6 ppm.

Dose-response formation of N7-(3-benzo[1,3]dioxol-5-yl-2-hydroxypropyl)guanine in liver and urine correlates with micronucleated reticulocyte frequencies in mice administered safrole oxide.

Safrole oxide (SAFO), a metabolite of naturally occurring hepatocarcinogen safrole, is implicated in causing DNA adduct formation. Our previous study first detected the most abundant SAFO-induced DNA adduct, N7-(3-benzo[1,3] dioxol-5-yl-2-hydroxypropyl)guanine (N7γ-SAFO-G), in mouse urine using a well-developed isotope-dilution high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (ID-HPLC-ESI-MS/MS) method. This study further elucidated the genotoxic mode of action of SAFO in mice treated with SAFO 30, 60, 90, or 120 mg/kg for 28 days. The ID-HPLC-ESI-MS/MS method detected N7γ-SAFO-G with excellent sensitivity and specificity in mouse liver and urine of SAFO-treated mice. Our data provide the first direct evidence of SAFO-DNA adduct formation in rodent tissues. N7γ-SAFO-G levels in liver were significantly increased by SAFO 120 mg/kg compared with SAFO 30 mg/kg, suggesting rapid spontaneous or enzymatic depurination of N7γ-SAFO-G in tissue DNA. Urinary N7γ-SAFO-G exhibited a sublinear dose response. Moreover, the micronucleated peripheral reticulocyte frequencies increased dose-dependently and significantly correlated with N7γ-SAFO-G levels in liver (r = 0.8647; p < 0.0001) and urine (r = 0.846; p < 0.0001). Our study suggests that safrole-mediated genotoxicity may be caused partly by its metabolic activation to SAFO and that urinary N7γ-SAFO-G may serve as a chemically-specific cancer risk biomarker for safrole exposure.

Synthesis of Upper-Rim Sulfanylpropyl- and p-Methoxyphenylazo-Substituted Calix[4]arenes as Chromogenic Sensors for Hg2+ and Ag+ Ions.

A series of calix[4]arenes with upper-rim sulfanylpropyl and p-methoxyphenylazo groups (compounds 8-10) were synthesized and found to be effective chromogenic sensors for selectively detecting Hg2+, Hg+, and Ag+ ions among 18 screened metal perchlorates. In comparison to previously reported diallyl- and dithioacetoxypropyl-substituted calix[4]arenes (5, 6, 14, 15, and 16) and the newly synthesized compound 7, the distal (5,17)-disulfanylpropyl-substituted di-p-methoxyphenylazocalix[4]arene 9 demonstrated superior performance with a limit of detection of 0.028 µM for Hg2+ ions in a chloroform/methanol (v/v = 399/1) cosolvent. Job's plot revealed 1:1 binding stoichiometry for all these upper-rim sulfanylpropyl- and p-methoxyphenylazo-substituted calix[4]arenes 8-10 with Hg2+ ions, and Benesi-Hildebrand plots from ultraviolet/visible (UV-vis) titration spectra were used for the determination of their association constants. Our findings indicated that the distal orientation of two p-methoxyphenylazo and two sulfanylpropyl groups in calix[4]arenes 8-10 is more favorable for binding Hg2+ ions than the proximal (5,11-) orientation; moreover, the adjacent sulfanylpropyl groups exhibited superior coordination as ligands compared to the allyl and thioacetoxypropyl groups. Notably, compounds 8-10 displayed a comparable trend in their association with Ag+ ions, albeit with 1 order of magnitude lower binding constants and a distinct binding mode compared to Hg2+ ions. UV-vis spectroscopy, Job's plots, high-resolution mass spectrometry, and 1H nuclear magnetic resonance titration studies are presented and discussed.

Construction of Mechanically Interlocked Fluorescence Photoswitchable [2]Rotaxane with Aggregation-Induced Emission and Molecular Shuttling Behaviors.

Here, we report the design, synthesis, and optical behaviors of a multistimuli responsive [2]rotaxane system constructed from noncovalent interactions between diarylethene (DAE)-based axle and a tetraphenylethene (TPE)-based macrocycle using a snapping supramolecular assembly approach. The shuttling behavior of the macrocycle (Ring-TPE) between dialkylammonium and urea stations could be realized by the influence of acid-base stimuli using 1H NMR spectroscopy. Switching between the open-form (OF) [2]rotaxanes (DAE-R1-OF and DAE-R2-OF) is highly reversible using external chemical stimuli. These rotaxane systems exhibit enhanced blue fluorescence in their aggregation states despite being weak or nonemissive in solution. A significant increase in fluorescence emission intensity of typical TPE in DAE-R1-OF and DAE-R2-OF at ca. 467 nm was observed as the water content was increased to ≥70% in CH3CN/H2O solvent mixtures. However, the fluorescence emission of TPE at its maximum aggregation state (95% fw) could be rapidly quenched upon UV light irradiation due to a very efficient energy transfer from the excited TPE (donor) to the closed form of DAE (acceptor). In contrast, OF DAE does not affect the fluorescence of the TPE unit, which remains at high level. Furthermore, the [2]rotaxanes showed excellent photochromic and fluorescent properties in solution, making them suitable for information storage and reversible photo-patterning applications.

A highly selective chromogenic and fluorogenic chemodosimeter for dual detection of Cu2+ based on a redox-active calix[4]arene with isoxazolylchloroanthracene.

Calix[4]arene 1, with two lower-rim isoxazolylchloroanthracene groups, is shown to be not only a chromogenic but also a fluorogenic chemodosimeter for the selective sensing of Cu2+. The binding properties of ligand 1 and control compounds 2 and 3 toward metal ions in CH3CN/CHCl3 (v/v, 1 : 1) were investigated by UV-vis and fluorescence spectroscopy. The results showed that only ligand 1 was highly selective for Cu2+ ions. When complexed with Cu2+, ligand 1 displayed a new absorption band around 435 nm and the color of the solution changed from colorless to yellow. Furthermore, the fluorescence of ligand 1 was severely quenched by Cu2+ and the limit of detection (LOD) was determined to be 1.674 µM. Therefore, compound 1 is not only a chromogenic but also a fluorogenic sensor for the detection of Cu2+ ions over other metal ions examined. When complexed with ligand 1, Cu2+ was reduced to Cu+ by the free phenolic-OH of ligand 1 and concurrently the phenol was oxidized by Cu2+ to quinones. The 1H NMR, EPR, and FTIR spectra provided evidence for the redox behavior of ligand 1 with Cu2+. The isolation of calix[4]diquinone 8 and Cu(CH3CN)4ClO4 from the reaction of ligand 1 with Cu(ClO4)2 confirmed their redox reaction.

Stiff-Stilbene-Bridged Biscalix[4]arene as a Highly Light-Responsive Supramolecular Gelator.

A newly designed stiff-stilbene functionalized biscalix[4]arene in its cis form Z-1 could be near-quantitatively photoswitched to the trans-isomer E-1 under irradiation of 385 nm UV light. The trans-biscalix[4]arene E-1 was found to be a supergelator in nonpolar organic solvents, e.g., cyclohexane, hexane, pentane, and ether, with critical gelation concentrations as low as 0.2, 0.5, 0.5, and 0.4% w/v, respectively. The cis-trans configurational isomerism of biscalix[4]arene 1 resulted in distinct self-assembly modes, leading to interesting microscopic morphological changes from honeycomb and ringlike structures to rodlike dense fibrous networks.

1,3-Alternate Calix[4]arene Functionalized With Pyrazole and Triazole Ligands as a Highly Selective Fluorescent Sensor for Hg2+ and Ag+ Ions.

We report here the synthesis of a 1,3-alternate calix[4]arene 8, with bis-pyrazolylmethylpyrenes on the one end and bis-triazolylmethylphenyls on the other end, as a homoditropic fluorescent sensor for both Hg2+ and Ag+ ions. Calix[4]arene 3, with lower-rim bis-pyrazolylmethylpyrenes in cone conformation, was also synthesized as a control compound. UV-Vis and fluorescence spectra were used for metal ions screening, and we found that both ligands 8 and 3 showed strong excimer emission of pyrenes when they are as a free ligand in CHCl3/MeOH (v/v, 3:1) solution; however, they both showed a high selectivity toward Hg2+ and Ag+ ions with strong fluorescence quenching and yet with different binding ratios. The fluorescence of ligand 8 was strongly quenched by Hg2+ but was only partially quenched by Ag+ ions; however, the fluorescence of ligand 3 was strongly quenched by Hg2+, Ag+, and Cu2+ ions. Job plot experiments showed that ligand 8 formed a 1:2 complex with both Hg2+ and Ag+ ions; ligand 3 formed a 1:1 complex with Hg2+, but it formed a 2:3 complex with Ag+. The binding constant of ligand 3 with Hg2+ and Ag+ ions was determined by the Benesi-Hildebrand plot of UV-vis titration experiments to be 2.99 × 103 and 3.83 × 103 M-1, respectively, while the association constant of ligand 8 with Hg2+ and Ag+ was determined by Hill plot to be 1.46 × 1012 and 9.24 × 1011 M-2, respectively. Ligand 8 forms a strong complex with either two Hg2+ or two Ag+ ions using both the upper and lower rims of the 1,3-alternate calix[4]arene as the binding pockets; hence, it represents one of the highly selective fluorescent sensors for the homoditropic sensing of Hg2+ and Ag+ ions.

Chiral anion recognition using calix[4]arene-based ureido receptors in a 1,3-alternate conformation.

The introduction of chiral alkyl substituents into the lower rim of calix[4]arene immobilised in the 1,3-alternate conformation led to a system possessing a preorganised ureido cavity hemmed with chiral alkyl units in the near proximity. As shown by the 1H NMR titration experiments, these compounds can be used as receptors for chiral anions in DMSO-d 6. The chiral recognition ability can be further strengthened by the introduction of another chiral moiety directly onto the urea N atoms. The systems with double chiral units being located around the binding ureido cavity showed better stereodiscrimination, with the highest selectivity factor being 3.33 (K L/K D) achieved for N-acetyl-ʟ-phenylalaninate. The structures of some receptors were confirmed by single crystal X-ray analysis.

Diversiform Nanostructures Constructed from Tetraphenylethene and Pyrene-Based Acid/Base Controllable Molecular Switching Amphiphilic [2]Rotaxanes with Tunable Aggregation-Induced Static Excimers.

Dual-emissive tetraphenylethene (TPE) and pyrene-containing amphiphilic molecules are of great interest because they can be integrated to form stimuli responsive materials with various biological applications. Herein, we report the study of mechanically interlocked molecules (MIMs) with aggregation-induced static excimer emission (AISEE) property through a series of TPE and pyrene-based amphiphilic [2]rotaxanes, where t-butylcalix[4]arene with hydrophobic nature was used as the macrocycle. Evidently, by adorning TPE and pyrene units in [2]rotaxanes P1, P2, P1-b, and P2-b, they display remarkable emission bands in 70% of water fraction (fw) in tetrahydrofuran (THF)/water mixture, which could be attributed to the restricted intramolecular rotation of phenyl groups, whereas prominent blue-shifted excimer emission of pyrene started to appear as fw reached 80% for P1 and 90% for P1-b, P2, and P2-b, which was ascribed to the favorable π-π stacking and hydrophobic interactions of the pyrene rings that enabled their static excimer formation. The well-defined distinct amphiphilic nanostructures of [2]rotaxanes including hollowspheres, mesoporous nanostructures, spheres, and network linkages can be driven smoothly depending on the molecular structures and their aggregated states in THF/water mixture. These fascinating diversiform nanostructures were mainly controlled by the skillful manner of reversible molecular shuttling of t-butylcalix[4]arene macrocycle and also the interplay of multinoncovalent interactions. To further understand the aggregation capabilities of [2]rotaxanes, the human lung fibroblasts (MRC-5) living cell incubated with either P1, P2, P1-b, or P2-b was studied and monitored by confocal laser scanning microscopy. The AISEE property was achieved at an astonishing level by integrating TPE and pyrene to MIM-based reversible molecular switching [2]rotaxanes; furthermore, distinct nanostructures, especially hollowspheres and mesoporous nanostructures, were observed, which are rarely reported in the literature but are highly desirable for future applications.

Controlled Sol-Gel and Diversiform Nanostructure Transitions by Photoresponsive Molecular Switching of Tetraphenylethene- and Azobenzene-Functionalized Organogelators.

The implementation of stimuli-responsive materials with dynamically controllable features has long been an important objective that challenges chemists in the materials science field. We report here the synthesis and characterization of [2]rotaxanes (R1 and R1-b) with a molecular shuttle and photoresponsive properties. Axles T1 and T1-b were found to be highly efficient and versatile organogelators toward various nonpolar organic solvents, especially p-xylene, with critical gelation concentrations as low as 0.67 and 0.38 w/v %, respectively. The two molecular stations of switchable [2]rotaxanes (R1 and R1-b) can be revealed or concealed by t-butylcalix[4]arene macrocycle, thus inhibiting the gelation processes of the respective axles T1 and T1-b through the control of intermolecular hydrogen-bonding interactions. The sol-gel transition of axles T1 and T1-b could be achieved by the irradiation of UV-visible light, which interconverted between the extended and contracted forms. Interestingly, the morphologies of organogels in p-xylene, including flakes, nanobelts, fibers, and vesicles depending on the molecular structures of axles T1 and T1-b, were induced by UV-visible light irradiation. Further studies revealed that acid-base-controllable and reversible self-assembled nanostructures of these axle molecules were mainly constructed by the interplay of multi-noncovalent interactions, such as intermolecular π-π stacking, CH-π, and intermolecular hydrogen-bonding interactions. Surprisingly, our TPE molecular systems (R1, R1-b, T1, and T1-b) are nonemissive in their aggregated states, suggesting that not only fluorescence resonance energy transfer but also aggregation-caused quenching may have been functioning. Finally, the mechanical strength of these organogels in various solvents was monitored by rheological experiments.

Light-driven nanofiber and nanoring morphological transformations in organogels based on an azobenzene-bridged biscalix[4]arene.

The morphologies of an azobenzene-bridged biscalix[4]arene organogel in different organic solvents can be photo-reversibly switched between nanofibers and nanorings as well as between closed and open-form vesicles.

Photocontrolled Supramolecular Assembling of Azobenzene-Based Biscalix[4]arenes upon Starting and Stopping Laser Trapping.

Laser trapping in chemistry covers various studies ranging from single molecules, nanoparticles, and quantum dots to crystallization and liquid-liquid phase separation of amino acids. In this work, a supramolecular assembly of azobenzene-based biscalix[4]arene is generated in ethyl acetate using laser trapping; its nucleation and growth are elucidated. No trapping behavior was observed when a 1064 nm laser beam was focused inside of the solution; however, interesting assembling phenomena were induced when it was shined at the air/solution interface. A single disk having two layers was first prepared at the focal point of ∼1 µm and then expanded to the size of a few tens of micrometers, although no optical force was exerted outside of the focal volume. Upon switching the trapping laser off, needles were generated at the outer layer of the assembly, giving a stable sea urchin-like morphology to the generated assembly. At a 30-50% dilution of the initial solution in ethyl acetate, a mushroom-like morphology was also observed. Laser trapping-induced assembly of azobenzene-based biscalix[4]arene was quite different from the sharp-ellipsoidal aggregates obtained by the spontaneous evaporation of the solution. These trapping phenomena were specifically observed for biscalix[4]arene in the trans conformation of azo-benzene moiety but not for the cis-form, suggesting that the laser trapping of this azobenzene-based biscalix[4]arene is photocontrollable. Dynamics and mechanism of the supramolecular assembling are considered, referring to laser trapping-induced nucleation and liquid-liquid phase separation of amino acids.

Skeletally Diverse Synthesis of Innovative [2,1-c]-1,4-Oxazepine and [1,4]-Quinoxaline Systems.

An efficient, innovative synthesis of [2,1-c]-1, 4-oxazepine and [1,4]-quinoxaline heterocycles along with the embodied pyrimido-pyrrolo motifs was established. Initially, the pyrrole ring was installed using microwave irradiation through an intramolecular base-catalyzed cyclization between acetyl bromomethyl pyrimidine dione and o-amino phenyl methanol or o-phenylenediamine methyl benzoates. Furthermore, oxazepine, and quinoxaline scaffolds were constructed by an acid-catalyzed condensation with a variety of aldehydes by an unconventional Pictet-Spengler reaction strategy. An important aspect of this work is to build novel heterocyclic ring systems with potential medicinal interest.

Study of urinary 2-{[2-(acetylamino-2-carboxyethyl]sulfanyl}butanedioic acid, a mercapturic acid of rats treated with maleic acid.

Maleic anhydride was reported illegally adulterated into starch to prepare traditional foods for decades in Taiwan. Maleic acid (MA), hydrolyzed from maleic anhydride, could cause kidney damages to animals. The potential health effects due to long-term MA exposures through food consumption have been of great concerns. Assessment of the dietary MA exposures could be very difficult and complicated. One of the alternatives is to analyze an MA-specific biomarker to assess the daily total MA intake. Therefore, this paper aimed to study the mercapturic acid of MA, 2-{[2-(acetylamino)-2-carboxyethyl]sulfanyl}butanedioic acid (MAMA), with our newly-developed isotope-dilution online solid-phase extraction liquid chromatography tandem mass spectrometry (ID-SPE-LC-MS/MS) method. MAMA was first synthesized, purified, and characterized with NMR to reveal two diastereomers and used for developing the analytical method. The method was validated to reveal excellent sensitivity with a LOD at 16.3ng/mL and a LOQ at 20.6ng/mL and used to analyze MAMA in urine samples collected from Sprague-Dawley rats treated with a single dose of 0mg/kg, 6mg/kg, and 60mg/kg (n=5) of MA through gavage. Our results show dose-dependent increases in urinary MAMA contents, and 70% MAMA was excreted within 12h with no gender differences (p>0.05). A half life of urinary MAMA was estimated at 6.8h for rat. The formation of urinary MAMA validates it as a chemically-specific biomarker for current MA exposure. Future study of MA metabolism in vivo will elucidate mechanisms of MAMA formation, and analysis of this marker in epidemiology studies could help to shed light on the causal effects of MA on human.

Excimer emission properties on pyrene-labeled protein surface: correlation between emission spectra, ring stacking modes, and flexibilities of pyrene probes.

The excimer emission of pyrene is popularly employed for investigating the association between pyrene-labeled biomolecules or between pyrene-labeled places in a biomolecule. The property of pyrene excimer emission is affected by the fluctuation in ring stacking modes, which originates from the structural flexibilities of pyrene probes and/or of labeled places. Investigations of the excimer emission in terms of dynamics of pyrene stacking modes provide the detailed spatial information between pyrene-labeled places. In order to evaluate the effects of probe structures and fluctuation in pyrene-pyrene association modes on their emission properties on protein surface, three types of pyrene probe with different linker lengths were synthesized and conjugated to two cysteine residues in the A55C/C77S/V169C mutant of adenylate kinase (Adk), an enzyme that shows a structural transition between OPEN and CLOSED forms. In the CLOSED form of Adk labeled by a pyrene probe with a short linker, excimer emission was found to be predominated by the ground-state association of pyrenes. The pyrene stacking structure on the protein surface was successfully determined by an X-ray crystallographic analysis. However, the emission decay in the protein suggested the existence of several stacking orientations in solution. With the increase in the linker length, the effect of fluctuation in pyrene association modes on the spectral properties distinctly emerged at both ground and excited states. The combination of steady-state and time-resolved spectroscopic analyses is useful for differentiation in the origin of the excimer emission, which is essential for precisely understanding the interaction fashions between pyrene-labeled biomolecules.

Anthryl-1,2,4-oxadiazole-substituted calix[4]arenes as highly selective fluorescent chemodosimeters for Fe(3+).

Fluorescent chemosensors 1 and 2, with 1,2,4-oxadiazoles as the binding ligands and anthracene as the fluorophore, were synthesized through sequential 1,3-dipolar cycloaddition reactions of 25,27-dioxyacetonitrilecalix[4]arenes 8 and 11. The fluorescence of 1 was severely quenched by both Fe(3+) and Cu(2+) , whereas that of 2 was selectively quenched only by Fe(3+) . Control compound 4 was also selectively quenched by Fe(3+) , which implied the importance of anthryl-1,2,4-oxadiazole core; furthermore, it was shown to give various oxidation products such as oxanthrone 13, anthraquinone 14, and imidazolyl oxanthrone 15. In addition to product separation and identification, the fluorescent quenching mechanism of these 9-anthryl-1,2,4-oxadiazolyl derivatives by Fe(3+) is also discussed. Furthermore, it should be noted that the oxadiazole-substituted anthracene 4 and calix[4]arene 2 are Fe(3+) -selective fluorescent chemodosimeters without the interference by Cu(2+) .

Potential Association of Urinary N7-(2-Carbamoyl-2-hydroxyethyl) Guanine with Dietary Acrylamide Intake of Smokers and Nonsmokers.

Acrylamide (AA), a rodent carcinogen, is widely used in industry and present in cigarette smoke as well as in foods processed at high temperatures. The metabolic activation of AA to glycidamide (GA) could be critical for AA carcinogenicity since GA causes DNA adduct formation in vivo. N7-(2-carbamoyl-2-hydroxyethyl) guanine (N7-GAG), the most abundant DNA adduct of AA, is subjected to spontaneous and enzymatic depurination and excreted through urine. Urinary N7-GAG analysis can confirm AA genotoxicity and identify active species of AA metabolites in humans, thereby serving as a risk-associated biomarker for molecular epidemiology studies. This study aimed to develop an isotope-dilution solid-phase extraction liquid chromatography tandem mass spectrometry method to comparatively analyze urinary N7-GAG levels in nonsmokers and smokers. Urinary N-acetyl-S-(propionamide)-cysteine (AAMA), a metabolite of AA, was also analyzed as a biomarker for current AA exposure. Urinary N7-GAG was quantified by monitoring m/z 239 → 152 for N7-GAG and m/z 242 → 152 for (13)C3-labeled N7-GAG under positive electron spray ionization and multiple reaction mode. The median urinary N7-GAG level was 0.93 µg/g creatinine in nonsmokers (n = 33) and 1.41 µg/g creatinine in smokers (n = 30). Multiple linear regression analysis of data revealed that N7-GAG levels were only significantly associated with AAMA levels. These results demonstrate that urinary N7-GAG of nonsmokers and smokers is significantly associated with a very low level of dietary AA intake, assessed by analyzing urinary AAMA.

Deformative transition of the Menschutkin reaction and helical atropisomers in a congested polyheterocyclic system.

A 4,7-phenanthroline polycyclic 1A designed for probing the limits of the Menschutkin reaction was synthesized in a six-step sequence. The rotational barrier of the phenyl ring nearby the N-methyl group in rac-2A was estimated to be ≫ 18.1 kcal/mol from VT-NMR experiments, making them a new type of helical atropisomer. The methylation rate constants of 9 and 1A with MeI was found to be 2.22 × 10(-4) and 9.62 × 10(-6) s(-1) mol(-1) L, respectively; thus, the formation rate of (P/M)-2A is one of the slowest rates ever reported for a Menschutkin reaction. The N-methyl protons in (P/M)-2A exhibit a significant upfield shift (Δδ 1.0 ppm) in its (1)H NMR, compared to those without a nearby phenyl, indicating a strong CH-π interaction is involved. Conformational flexibility in dipyridylethene 9 is clearly shown by its complexation with BH3 to form helical atropisomers (P,P/M,M)-10. The pKa values of the conjugate acids of 1A and 9 in acetonitrile were determined to be 4.65 and 5.07, respectively, which are much smaller compared to that of pyridine 14a (pKa = 12.33), implying that the basicity, nucleophilicity, and amine alkylation rates of 1A and 9 are markedly decreased by the severe steric hindrance of the flanking phenyl rings in the polyheterocycles.

Different sensing modes of fluoride and acetate based on a calix[4]arene with 25,27-bistriazolylmethylpyrenylacetamides.

25,27-Bis{1'-N-(1-pyrenyl)-aminocarbonylmethyl-1H-[1',2',3']tri-azolyl-4'-methoxy}-26,28-dihydroxycalix[4]arene, 4, is synthesized as a fluorescent chemosensor for the selective detection of both anions and ion pairs in MeCN. Sensor 4 uses bis-triazoles as ligands to bind a metal ion, bis-amides and bis-triazoles as the sites to recognize anions, and pyrenes as fluorophores. Among eight anions screened, chemosensor 4 showed a marked fluorescence change toward F(-), H2PO4(-) and AcO(-), but 4 responded to each anion in a distinct way. In the presence of F(-) at low concentrations, the dynamic excimer emission of compound 4 at λ(max) 482 nm was quenched, but an emission at λ(max) 472 nm appeared at large doses of F(-). A control compound 6 showed very similar red shifts in the UV-vis and excitation spectra as 4 did, and its 472 nm emission band grew as the fluoride doses increased. Thus, the growth of the 472 nm emission of 4 and 6 in the presence of excess F(-) may be because strong H-bonding interactions of amido protons with F(-) favoured the formation of pyrene dimers in the ground state with charge transfer characteristics. The addition of H2PO4(-), unlike F(-), to a solution of 4 showed an enhanced monomer emission but a decreased excimer emission (λ(max) 482 nm). Adding AcO(-) to 4 produced a systematic change from a dynamic excimer (λ(max) 482 nm) to λ(max) 472 nm but with very little change in the UV-vis spectrum. Time-resolved fluorescence measurements on compound 6 with F(-) and AcO(-) confirmed that the 472 nm emission band mainly came from static excimers for the former, but was partly from a dynamic excimer for the latter because it contained a growth component in the fluorescence decay traces. Without pre-treatment with an anion, chemosensor 4 showed recognition of only metal ions Cu(2+), Hg(2+) and Cr(3+), but it became sensitive to Ag(+) when it was pretreated with fluoride.

The synthesis of rigid polycyclic structures for the study of diatropic or steric effects of a phenyl ring on CF bond.

Polycyclic compounds 1a-c were synthesized to study the diatropic effects of a flanking phenyl ring on nearby CH and CF bonds. (19)F NMR spectra of 1b and 1c were strongly deshielded compared with those of the ring-opened compounds 3b, 7b, and 7c. DMol3 calculations on 1a-c provided quantitative bond lengths and torsional angles to support the conclusion that the downfield shifts in the (19)F NMR spectra are mainly due to steric interactions between the CF bonds and the π clouds of the phenyl ring(s).